The invention concerns a one-stage or multi-stage high-pressure centrifugal pump unit of the vertical or horizontal type, for the delivery of liquids to higher delivery heads.
The pumps of centrifugal pump units for the delivery of liquids to higher delivery heads are in the great majority designed as multi-stage centrifugal pumps with up to fifteen stages. The electrical prime mover mainly used is a three-phase asynchronous motor with the upper limit speeds of n.sub.syn =3000 min.sup.-1 at 50 Hz, European grid and n.sub.syn =3000 min.sup.-1 at 60 Hz, North American grid, being determined by the grid frequency. It is also customary to arrange a transmission between the electrical prime mover and a multi-stage centrifugal pump, in order to increase the speed and to reach a pump drive speed higher than n=3000 min.sup.-1. (Technisches Handbuch Pumpen, VEB Verlag Technik Berlin, 5. Auflage 1976; Kleines Pumpenhandbuch fur Chemie und Technik, Verlag Chemie GmbH, Weinheim 1967). Other prime movers, such as internal combustion engines and turbines are also being used.
The disadvantage of these pump units lies primarily in the fact that with the design size as applied to the customary design of pump units, it is not possible to attain a greater delivery head concurrently with maintaining a good degree of efficiency, good suction, and reliable operation at a manufacturing expense that can be economically justified. The manufacturing expenditure will be too high relative to the time required for manufacture, the expenditure for materials and the dimensions.
The known multi-stage types of pumping unit of conventional design, representing the present state of the art thus are no solutions with optimal economics. Added to this, the operating characteristics, especially vibration and wear characteristics, are not satisfactory. There have been recent endeavors to eliminate the acceptance of disadvantages in the design of pumping units with multi-stage centrifugal pumps, by using high-speed single-stage centrifugal pumps. Proceeding from the fact that with a given output the impeller diameter becomes smaller with increased drive speeds, the entire pump unit will become more compact, more economical in manufacturing, procurement, installation, and also operation with higher intended drive speeds, with a concomitant improvement of the operating characteristics. These deliberations have lead to the development of a known high-speed, one-stage or two-stage transmission-driven pump for outputs of V up to 160 m.sup.3 /h and H up to 1700 m.
The disadvantages of a relatively poor suction are reduced herein by an inducer arranged prior to the high-pressure stage. The pump has electric drive by a three-phase asynchronous motor. The suction stage (inducer) and the high-pressure stage are on a common shaft and rotate at the same speed. The transmission, arranged vertically between the centrifugal pump and the drive motor, will increase the motor speed of N=3000 min.sup.-1 to output speeds of the magnitudes of about N=40,000 min.sup.-1. Instruments to monitor the operating conditions are arranged within the transmission. A metering oil pump maintains a continual circulation of lubricating oil within the transmission. The lubricating oil is regenerated by filters and heat exchangers (Kleines Pumpen Handbuch fur Chemie und Technik Verlag Chemie GmbH, Weinheim 1967). An improvement in the construction of the transmission has led to elimination of the oil pump and the heat exchanger, the high speed up to n=40,000 min.sup.-1 notwithstanding (German Letter of Disclosure No. 22 13 731). The demand for a modification of the delivered flow of a centrifugal pump unit already installed in an industrial plant is met, within defined limits, in the first line by applying the uneconomical throttle regulation.
Infinitely variable speed regulation, with low losses in considerably more economical than throttle regulation. With multi-stage or single-stage centrifugal pump units, economical infinitely variable flow regulation is, f.i., not readily possible with the known electric prime movers. All mechanical and electrical devices known hitherto for infinitely-variable speed regulation, such as f.i. fluid couplings, variable-speed transmissions, high-frequency motors with frequency converter, direct-current motors with mercury-vapor rectifier, et al, are economically expensive solutions.